The unit pictured to the right is a stock HF85 which is need of a complete restoration.This one was dirty, had surface rust and only one channel worked properly and had hum in the background.So this one will bet a complete strip down of the unit down to the bare chassis and rebuild it from the ground up.
If you have an Eico manual follow to it for all the wire paths.It is important to do this as sometimes, rewiring can cause stray hum to appear due to heater wiring and some strange ground loops.
If you can't get a construction manual, take some pix before disassembling. I cleaned the bare chassis using an automotive type of mag wheel cleaner. This leaves the cleaning cloths black in color and really works. Next I installed Belton tube sockets/new shields for the phono stage and new hardware if required to replace the rusted out screws.
After reinstalling the sockets and terminal strips I rewire all the heater wiring with stranded 22 guage wire.
The power supply was the next item I started to rebuild. The original can cap needed replacing. The stock one is 20uF/400v, 40uF+ 40uF /350v.
Easiest way is to install a JJ or F&T 50uf/50uf/@500v and add another 50-100uf below the chassis. The 3 section ones are extremely expensive. Hamseed Hamfest can make a custom one for around $35-$40+shipping(see HF81 tab for one)
At right the unit has been rewired, Kiwame 2 W carbon film resistors in the plates and rest of the resistors are carbon film.
K40 PIO coupling capacitors used in the signal paths. I find these have excellent detail/soundstage for the money.
See the HF81 rebuild as Mundorf's were used in the preamp section. Those are a big step up from the PIO but at almost 10X the cost.
The original RCA jacks on the preamps were just horrible. First they are too close together to fit some of the larger connectors on todays modern cables . They are usually bent and corroded . Lastly there are many unused inputs like mike input, am, etc. What I did was to remove all the old rca jack boards and made up new boards with gold rca jacks. The rca jacks get replaced for pre-out, line out, AM-FM, Aux 1 and Aux 2 and phono. This gives you 3 line level inputs and 1 phono input.
The input selector switch was removed and a similar 6x2 switch is used and the old selector control removed. The original selector switch also has RIAA filters, which are a combination of resistors and capacitors in series/parallel mounted on the original switch. There are also a few other caps etc, that were originally used for mike inputs etc. With the original control, when you select an input that uses the phono/mike, depending which input you choose, a filter is selected to equalize that input. In the case of the phono, LP records are manufactured with extended highs. If a phono cartridge is fed directly into a line stage , you would hear the sound being very tinny and trebly. So a phono stage has to equalize the output of the phono cartridge and then produce gain to be at the same level as the other inputs feeding into the line stage of the preamp. What I did was to feed the input cable from the rca phono jacks directly to the input of the 12ax7 phono tube. I then installed the RIAA components directly on the terminal boards. The output from the phono stage now connects as an input into the selector switch. Also the blend switch was bypassed and now the output from the new selector switch goes directly to the input of the volume control. Below shown is a ALPS 500k volume pot to replace the original pot if it has failed with one of the sections. The shaft on the ALPS is a straight shaft and the original 2 piece volume knobs can no longer be used. A knob with a 1/4" shaft hole needs to be sourced or what I did one unit was to use the Eico knob off an HF12 amplifier with the spline, and then cutoff the ALPS pot and added a shaft coupler with a spline end to fit the knob. The HF81 tab shows one for a different knob but this gives an idea what is involved.
The HF85 pictured to the right was purchased as an unfinished kit, complete with every resistor, nuts and bolts and tubes. Someone started to mount the tube sockets on the chassis and it was never completed and sat for over 40 years.
I completed the build but used all premium parts to complete.
Below are a few other pix of some other HF85 restoration projects.
The newest HF85 which I restored had a rare wood cabinet. These were available from Eico as an upgrade. This also has the fuse holder which I haven't shown in other pictures. These preamps did NOT have fuse for the AC. I remove the one ac power plug, close off the hole and insert a flat chassis mounted fuse holder.